According to optometrist Dr. Troy L. Bedinghaus on About.com, the eyes sometimes develop a different color due to hyperbilirubinemia and subconjunctival hemorrhage. Yellow eyes, also called icterus, result from a buildup of bilirubin in the eyes.
Hyperbilirubinemia is an increase in levels of bilirubin, a brownish yellow substance in bile that breaks down fats, explains Dr. Bedinghaus. The body produces bilirubin when the liver breaks down old red blood cells and removes it through stool. This substance tends to accumulate quickly when an unusually high number of red blood cells is broken down. Common causes of high bilirubin levels are liver disease and jaundice, which causes the eyes and skin to turn yellow.
According to Dr. Bedinghaus, another cause of eye discoloration is subconjunctival hemorrhage, also known as eye bleed, a condition that typically results in a visible red pool of blood in the eye. The white part of the eye, called sclera, is protected by the tissue known as conjunctiva. This tissue also lines the inside of the eyelid and covers thin, fragile blood vessels that easily burst or break. Blood leaks out when they break and remains between the sclera and the conjunctiva. A small leak causes part of the eye to appear red, while a large leak causes the entire white part of the eye to appear completely blood red.